About 300 members of the Wellington Tramways and Public Passenger Transport unions attended a stop-work meeting in Kilbirnie today to discuss the effects of phasing out trolleys.

Greater Wellington Regional Council is expected to sign off on a plan tomorrow that will see the capital's 60 trolley buses scrapped in 2017 and replaced with hybrid diesel-electric buses.

The city's other 218 diesel buses will suffer the same fate but will be progressively phased out as they reach their end of their useful lives.

The unions' concern is that with trolley buses out of the mix their owner, NZ Bus, will be at greater risk of losing contracts to rival bus companies.

That could mean NZ Bus has to resort to job cuts or winding back its terms and conditions in order to stay competitive.

Two motions received unanimous support from union members today.

One was for the union to urge the council to delay its decision on scrapping the trolleys until the region was ready for fully electric buses and the technology had been proven in Wellington.

The other was for the council to put provisions in place protecting current wages and conditions for drivers regardless of which bus company it awards contracts to from 2017.

Paul Swain, the regional council's transport portfolio leader, fielded questions at the meeting but did not always have answers the crowd was looking for.

He said it was not the council's place to determine wages and conditions. Rather, it was a matter for unions and bus operators.

But bus operators would be looked upon more favourably during tendering if they had a good working relationship with their workforce, because that meant they would be less susceptible to strikes, he said.

If the process was done right then the council would be able to put a more attractive bus network in place, which would see demand increase and hopefully prevent any job cuts.

Swain also defended the decision to scrap trolley buses, saying the council was not prepared to spend $52 million ratepayer dollars upgrading their power supply and substations.

Tramways Union secretary Kevin O'Sullivan said he was pleased so many members showed up to make their voices heard on the issue.

He was confident the unions would prevail regardless of whether the regional council included the demands in its transport plan tomorrow.

''We keep getting told there's no reason why wages and conditions can't be stipulated in these new contracts.''